Unusual Hafnium–Pyridylamido/ER_n Heterobimetallic Adducts (ER_n=ZnR₂ or AlR₃)

Abstract

NMR spectroscopy and DFT studies indicate that the Symyx/Dow Hf(IV)-pyridylamido catalytic system for olefin polymerization, [{N(-),N,CNph(-)}HfMe][B(C6F5)4] (1, Nph = naphthyl), interacts with ER(n) (E = Al or Zn, R = alkyl group) to afford unusual heterobimetallic adducts [{N(-),N}HfMe(μ-CNph)(μ-R)ER(n-1)][B(C6F5)4 in which the cyclometalated Nph acts as a bridge between Hf and E. (1)H VT (variable-temperature) EXSY NMR spectroscopy provides direct evidence of reversible alkyl exchanges in heterobimetallic adducts, with ZnR2 showing a higher tendency to participate in this exchange than AlR3. 1-Hexene/ERn competitive reactions with 1 at 240 K reveal that the formation of adducts is strongly favored over 1-hexene polymerization. Nevertheless, a slight increase in the temperature (to >265 K) initiates 1-hexene polymerization.

Selectively Measuring π Back‐Donation in Gold(I) Complexes by NMR Spectroscopy

“…The rotation rate constant (k r ) of the pyrrolidine, which is related to the CÀN bond order, [39] was obtained using the VT-1 H-EXSY NMR technique, which already proved to be effective in the measurement of activation parameters. [40][41][42] The measurement of k r is based on the exchange of the nonequivalent protons A and B of the pyrrolidine ring, due to the rotation around the CÀN bond. This gives two off-diagonal peaks in the 2D spectra ( Figure 3 a and b, example for complex 9), the volume of which is related to the rotation rate (see the Experimental Section and Supporting Information).…”

Interception of Elusive Cationic Hf–Al and Hf–Zn Heterobimetallic Adducts with Mixed Alkyl Bridges Featuring Multiple Agostic Interactions

“…The two singlets at d H = À0.62 and À0.67 are assigned to the terminalA l-bound methyl moieties because of their scalar coupling with the carbon signals at d C = À5.55 and d C = À6.75, respectively.T he chemical shifts of the remaining methyl group (d H = 0.31, d C = 40.6) support assignment as the bridging moiety( Me18, Figure 1). Startingf rom H9, protona nd carbon resonances of the Cp ligand bearing the nonmetalatedp ropylc hain (10)(11)(12)(13)(14)(15)(16) are individuated by following the scalar connectivity in 1 HCOSY, 1 H, 13 CHSQC, and 1 H, 13 CHMBC NMR spectra. The assignments of resonancesb elongingtothe metalatedC pligand follow the same line of reasoningb ys tarting from the methylene carbon (C1, d C = 57.6).…”

“…[7a, d, 8] Crystallographic characterization has also been reported for af ew heterobimetallic species featuring two bridging methylg roups. [9] In contrast, detailedr e-ports of speciesw ith bridginga lkyls longer than methylo r with inequivalent bridging alkyls(X¼ 6 Y, Scheme1)are extremely rare, [10] despite the critical roles ascribed to them in processes such as CCTP,CSP,and olefin polymerization.…”

NMR and EPR trapping of the active species in the ethylene polymerization and trimerization catalyst systems

“…The concentration of 16 decreased with time (Fig. 10b) (14) Ar−CH 3 (15) Ar−CH 3 (14) system 11/MMAO has produced a much higher amount of PE and lower amount of 1-hexene than the system of 11/MAO [10]. As noted above, the major part of titanium exists in the catalyst system 11/MMAO, in the form of Ti III species.…”

“…This tendency supports stable interest to the detailed mechanistic studies of metallocene and post-metallocene catalyzed polymerization [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. However, quite often the available information on the reaction mechanism remains insufficient.…”